Process for the sealing and internal repair of systems of laid conduits

ABSTRACT

A process for the sealing and internal repair of systems of laid conduits in which a sealant is introduced into the leaky conduit by means of water, the sealant being a finely divided, inert material. The conduit is emptied and compressed air charged with particles of an abrasive substance is blown through it. The conduit is then internally coated by blowing into it a solvent-free epoxy resin containing a hardener and fibers. Alternatively, the sealant is introduced into the leaky conduit by means of air, the sealant being dry, finely ground, water-swellable bentonite; a dry, hydraulically disintegratable plastic dispersion preparation; or a mixture thereof. The conduit is then filled with a fluid, the fluid being either water or a mixture of steam and air.

This is a divisional of application Ser. No. 08/186,440 filed Jan. 25,1994 now U.S. Pat. No. 5,999,659, which is a divisional of applicationSer. No. 07/838,191, filed as PCT/EP91/01210 Jun. 27, 1991.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a process for the sealing and internalrepair of systems of laid conduits having a small internal diameter, inwhich sealing is carried out by blocking a leak by means of anintroduced sealant and internal repair is carried out by abrasivelyblowing out and recoating of the conduit with resin material. Suchconduits are, for example, feed and discharge conduits for water or gasin residential, industrial and municipal installations up to a diameterof about 200 mm; this includes domestic and industrial sewage conduitsup to the mains.

2. Brief Description of the Prior Art

The problem of damage and encrustation of such conduits has been knownfor a long time. Such damage is due, among other things, to corrosion,movement and vibration of the earth round the conduits; encrustationsare due, in particular, to lime deposits from the water, to rustformation in the conduit, to other deposits from the water, to reactionproducts between substances entrained in the water and the conduit metaletc. Combinations of the above-mentioned effects are also known.

This damage or these encrustations are particularly undesirable in thecase of conduits which are fixed in a wall or laid in the ground; ofcourse conduits are usually laid in this manner nowadays.

Sealing and blocking techniques for laid conduits are also known fromthe patent literature:

U.S. Pat. No. 3,287,148 teaches a process for sealing laid gas conduitsby blowing in a foamed sealing emulsion. The foam settles on theinternal wall and condenses there. In the case of leaks, it tends tosettle in larger quantities.

This method is expressly suited only to gas conduits; solid additions tothe sealing emulsion are neither taught nor made obvious.

The process according to U.S. Pat. No. 3,727,412 describes a repairprocess in which the conduit portion with the leak is sealed at thefront and rear. A specially stablised emulsion is then pressed in whichissues at the leak, is destabilised there and coagulates so that theleak is sealed.

Actual solid sealing materials are not therefore pressed in and thevehicle is water, not gas.

U.S. Pat. No. 4,311,409 teaches the sealing of leaks in laid conduits bymeans of very fine substances having a high capillary action. The veryfine substance is arranged externally at the leak and is watered there.The capillary pressure thus obtained counteracts the delivery pressureof the medium flowing in the conduit.

The very fine insulating material is laid onto the conduit from theexterior, after excavation of the leak (FIG. 1).

Finally, U.S. Pat. No. 4,503,613 describes a process and an apparatusfor the internal repair of laid conduits by means of "plastic mist"conveyed in a gas stream. It cannot be seen clearly from the patentspecification whether actual leaks are also sealed with it and,moreover, it does not appear immediately possible to produce the plasticmist.

Nowadays, laid utility conduits are also cleaned by means of compressedair with and without the addition of sand and reactive resins are alsoatomised by means of compressed air into conduits which have beenprecleaned in this way.

With a relatively known method of cleaning on a practical basis,compressed air is charged from optionally travelling compressorinstallations via a distributor into the conduit to be cleaned. In afirst phase, only air which has been heated by compression is predried.Sand is subsequently added in the air stream in a second phase. It isimportant that the air and sand mixture is guided with a spiral movementthrough the conduit; normal movement of the mixture is explicitlydescribed as ineffective. In a third phase of the known process, areactive resin is injected into the conduit and distributed therein,again by means of a spirally moved compressed air stream.

GB A 2 140 337 teaches such a process. A characteristic of this processis that both the cleaning stream and the resin through-put stream flowin a pulsating manner through the conduit to be repaired. Furthermore,the sizes and quantities of the abrasive particles added to the cleaningstream are not defined, and the addition of bonding agents with grainsizes which are also defined to the repair resin is not mentioned.

SUMMARY OF THE INVENTION

The process according to the invention for sealing, cleaning andre-coating the internal walls of utility water conduits differs from thediscussed methods basically in that it is optimised as an overallprocess and therefore also leads to rapid and reliable results.

The process according to the invention for the sealing and internalrepair of systems of laid conduits having a small internal diameter inwhich sealing is carried out by blocking the leakage by means of anintroduced sealant and internal repair is carried out by abrasiveblowing out and recoating of the conduit with resin material, ischaracterised by the following process steps:

after detection of one or more leakages in a portion of conduitand--optionally--after drying out the portion by means of heatedcompressed air

(a) either introduction and blowing in of a sealant containing dry, veryfinely ground, water-swellable bentonite and/or a hydraulicallydisintegratable plastic dispersion drying preparation as well as inertadditives, or introduction by means of water of finely divided inertmaterial having a specific gravity of 1±0.8 g cm⁻³ then after possiblyblowing through the conduit which is charged with the sealant and isoptionally emptied, by means of very finely divided abrasive substances,charging and holding the conduit with a steam/air mixture at >2 barexcess pressure or filling or perfusion with water in/through theconduit, if the introduced sealant was dry, and,

after detection of the improved impermeability of the conduit

(b) continuous blowing through of the conduit for internal cleaning withcompressed air which is charged with particles of abrasive substancehaving a Moh's hardness of >4 and an average grain size of <2 mm and--optionally--with a small content of said dry bonding agent, and,finally,

(c) introduction and blowing in of solvent-free epoxy resin mixturewhich contains the hardener and is loaded with cellulose fibres having alength of 40±10 mm and/or glass fibres having a length of 5±3 mm forinternally coating the conduit.

The leak in the portion of conduit can be detected by determining thepressure drop therein, by channel thermography or by channel TV.

In particular, the powdered dry sealant is poured into a conduitattachment, the conduit attachment is connected to the inlet of theportion of conduit and the sealant is either blown by compressed airinto the conduit and, while maintaining a pressure difference of >1 bar,is blown between inlet and outlet so that the sealant accumulates at theleakage point or--optionally--air is removed at the leakage pointseither by means of lances guided downwardly from the top at the leakagepoint or by means of lances pushed into the conduit and the accumulationof the sealant at the leakage point is thus promoted.

Next, the steam is fed into the compressed air conduit by means of aninjector and the conduit part to be repaired is perfused with thesteam/air mixture until the steam issues at the conduit end, whereuponthe pressure is built up in the conduit.

During the wet blocking operation, the finely divided inert agent isstirred in water and the mixture is continuously pressed in through theconduit while maintaining a pressure drop of >0.1 bar.

During the subsequent (and optional) abrasive blowing out operation, theair pressed through the conduit is continuously charged with theabrasive agent, and abrasive agent and removed lining material isfiltered from the air at the conduit outlet.

The dry sealant for blocking conduits to be repaired by means of air ischaracterised by contents

of very finely divided swellable bentonite of 30±20% by weight and/or

of very finely divided, hydraulically disintegratable, water-insolubleor water swellable dispersion dry preparation based on polyacrylic acidesters, styrene copolymers or PVAC copolymers of 20±8% by weight ashydraulically reacting binder.

In particular, said sealant is characterised by contents

of dried light expanded clay pellets of < 20 mm .O slashed._(A) and/or

of polystyrene foam beads of <6 mm .O slashed._(A) and/or

of cork particles of about <4 mm .O slashed._(A) and/or

of very finely divided diatomaceous earth (Aerosil®) of d>1 g.cm⁻³ asinert additives, wherein

to the hydraulically reacting binders, up to 10% by weight of their massof very finely ground Portland cement can be added.

The finely divided inert material for blocking conduits to be repairedin the water stream is characterised in that it contains and/or consistsof

fine beads of expanded clay or glass having a specific gravity <18 gcm⁻³,

plastics foam parts or cork particles having a specific gravity >0.2g.cm⁻³ and

very finely divided diatomaceous earth having a compactness ˜1.4 g.cm⁻³.

The application of the above-described process for the internal repairof laid conduit systems--in particular of water conduit networks--ischaracterised by the following process steps:

determination of a portion of a system, i.e. a group of supply conduitsto a conduit main line, which supply conduits have similar pressuredrops to the main line and open at substantially the same level into themain line plus the portion of the main line to the entry region of thefollowing group of supply conduits;

opening of the supply conduit ends and of the staged end of the mainline

connection of the compressed air conduits to the supply conduit endsand--optionally--to the more highly positioned main line portion and

implementation of the sealing and internal repair process according toone of the described methods.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a system of conduits with a main line from an inlet to anoutlet, and a number of supplied conduits with corresponding openings;

FIG. 2 shows another system of conduits with a main line from an inletto an outlet, and a number of supplied conduits with correspondingopenings;

FIG. 3 is a schematic representation of an apparatus for carrying outthe sealing and internal repair process of the present invention bymeans of compressed air;

FIG. 4 illustrates, schematically, a change-over valve arrangement,which may be employed in the apparatus shown in FIG. 3, for lump-wiseintroduction of the resin composition;

FIG. 5 illustrates, schematically, a change-over valve arrangement,which may be employed in the apparatus shown in FIG. 3, for spraying inthe resin composition;

FIG. 6 shows an installation for completion of the method according tothe present invention, in particular a seal technology, and showingthree layers of fine sand and gravel in a container, and a pipingarrangement; and

FIG. 7 shows an apparatus for carrying out the sealing and internalrepair process of the present invention by means of a water stream.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

This application advantageously occurs with those system portions whicheither comprise a main line 1.02 from inlet 1.12 to outlet 1.14 andsupply conduits 1.05 to 1.08 with the corresponding openings 1.15 to1.18 or a main line 2.02 from inlet 2.12 to outlet 2.14 and supplyconduits 2.05 to 2.08 with the corresponding openings 2.15 to 2.18.

When blowing out such system portions, the compressed air connectionsare arranged at 1.14 to 1.18 such that blowing is carried out in aco-current or counter-current, these connections being actuated by meansof change-over valves.

During the introduction of resin, the resin composition isadvantageously introduced into the blown out conduit in lump or atomisedform in predetermined quantities via the change-over valves and is blownthrough by compressed air.

The apparatus for carrying out the above-described sealing and internalrepair process by means of air comprises, in addition to a mobile aircompressor installation, an apparatus for charging the compressed airwith abrasive substances, an installation for mixing and optionally forconveying the resin compositions and an end separator for sand and resindroplets, in particular

a compressed air distributor 3.02 with air supply conduit 3.04 and airdelivery conduits 3.05 to 3.07, the conduits carrying valves andpressure measuring devices 3.15 to 3.27 among other things with whichapparatus it is possible--together with conventional attachments andpressure measuring devices--both to determine the pressure drop inindividual conduit lines at different p and m and also to drive theautomated repair programs.

The same apparatus also comprises change-over valves either with mainline 4.02, subsidiary line 4.04, the necessary valves 4.12 to 4.15 and aresin container 4.22 preferably with inspection glass, for the lump-wiseintroduction of the resin composition or with main line 5.02, subsidiaryline 5.04 with valves 5.14, 5.15 as well as resin container 5.22,preferably with inspection glass, and with ejector 5.32 for spraying inthe resin composition.

It can immediately be seen that such an apparatus can be equippeddirectly with a programmable measuring, calculating and regulatinginstallation for the automated implementation of the blowing out andresin introduction phases after determination of the stages, afterapplication of the connections and after input of the necessarycharacteristics.

The similar apparatus for carrying out the sealing and internal repairprocess by means of a water stream comprises, in addition to the usualfeed and discharge conduits, auxiliary devices etc., a pressurised watersupply (7.01), a silo (7.02) for the receiving and continuous deliveryof the finely divided inert materials, a feed and mixing section (7.03),a supply conduit for mixing with measuring devices (7.04) for theconduit (7.10) to be repaired, a delivery conduit (7.21) with collectingscreen or separator (7.22) and optionally return conduit (7.23) for thewater.

Examples illustrating the process according to the invention, theapparatus and the application will now follow (Examples 1 to 3 dryblocking, Example 4 wet blocking).

As Example 1 of the process according to the invention there is nowreported an application thereof for the cleaning of a supply waterconduit in a private swimming pool.

Preliminary inspection of the conduit revealed no leaks, impermeabilityor the like.

After closing all branches, the inlet and outlet of this conduit wereopened on the day beforehand.

On the working day itself, the conduit was first pre-dried withcompressed air from a compressor. The compressed air was pre-dried in amoisture extractor prior to admission into the conduit.

The necessary quantity of air emerged (as also for the cleaning andcoating afterward) from the following Table:

    ______________________________________                                        NW 25 mm/1"  Pipe length to 100 m                                                                         7.5     m.sup.3 /min                              NW 40 mm/11/2"                                                                             "              14.0    m.sup.3 /min                              NW 50 mm/2"  "              17.0    m.sup.3 /min                              NW 80 mm/3"  "              26.0    m.sup.3 /min                              NW 100 mm/4" "              30.0    m.sup.3 /min                              NW 150 mm/6" "              45.0    m.sup.3 /min                              ______________________________________                                    

In the present case, the total length of the conduit was about 80 m; itconsisted mainly of 11/2" and 2" pipes. The conduit was partially fixedin the wall and partially laid in the open in the sub-floor.

Preliminary drying lasted about 40 minutes. A special separator wasmounted at the conduit outlet; the issuing fine solid material(apparently mainly lime deposits and rust) passed into a specialseparator.

A feeder for the abrasive agent (dry normal sand of 2 to 4 mm withaddition of waste corundum of 1 to 2 mm grain size) was then fittedbetween compressor and air inlet into the conduit. A separator with acyclone divider with manometer and regulating valve was installed at theair outlet. The process was then carried out for about 12 minutes at anaverage excess pressure of about 1.2 bar with maximum compressor outputand addition of abrasive agent. After the blowing operation, about 300kg of sand had been blown through the conduit to be cleaned. At the endof the blowing operation, the air had a temperature of ˜60° C. as itissued from the separator.

After blowing out for a short period, 5 kg of adhesive resin having thefollowing formulation were prepared batchwise in each case; the resinwas prepared in each case such that it had a viscosity higher than 2.10⁴m Pa.s at about 25° C. The charges were then poured as lumps into theair inlet nozzle (vertically) at the beginning of the conduit. Thecompressed air was then immediately connected and the lumps blown inuntil no more clear resistance was detectable. A further lump of resinwas then introduced, and so on, five times in total. Only then was adelivery of resin from the end of the conduit detected.

Basic formulation of adhesive resin for coating:

    ______________________________________                                        Epoxy resin: Bis-A or Bis-A/F type                                                                 47%      by weight                                       Hardener: aliphatic polyamine adduct                                                               19%      by weight                                       Titanium dioxide     8%       by weight                                       Silicate filler      21%      by weight                                       Thixotropic material (Aerosil.sup.R)                                                               5%       by weight                                       Total                100%     by weight                                       ______________________________________                                    

Blowing through was then carried out for a further 30 minutes, and theconduit was sealed at the top and bottom at the end of the blowingperiod.

Two days later, the conduit was reconnected to the network andthoroughly flushed beforehand.

Filling of the tank after cleaning of the conduit lasted about 9 hoursand produced clear water; prior to cleaning, filling lasted more than 14hours and the water was sometimes rust red in colour.

Example 2

A y-part which was 60 m long in total, of an approximately 10 cmdiameter sewage conduit which extended from two EFH after the junctionunder a road with a height difference of about 3 m and a total of foursubstantially 90° bends exhibited a leakage (obvious loss of water) intothe main at the entrance on inspection.

This conduit part was sealed at the two entrances into the EFH and wasconnected at the outlet (i.e. at the entrance into the main, this pointbeing exposed owing to a new construction) to a compressed airdistributor according to FIG. 3 connected to the mobile compressor. Itcould then be detected that an excess pressure of about 0.2 bar couldnot be maintained in the conduit part (confirmation of the leak andsimultaneous identification thereof as gas permeable).

The following sealant was poured, after thorough mixing, into a portionof conduit having a length of 1 m and a diameter of 10 cm, which couldbe inserted tightly between conduit end and outlet of the compressed airconduit at the distributor:

about 5 l of Styropore beads .O slashed._(A) ˜2 cm, dry,

about 1 l of Mowilith® powder DM 200P,

about 50 g of PC 300Z.

The mixture was blown by means of compressed air into the conduit to berenewed. It was found that owing to slight opening of the closures atthe two entrances, the blowing in of the sealant took place more easily(P˜1 bar excess pressure). This blowing in operation was repeated fourtimes.

The conduit part was then filled from the outlet with water and was leftfor about 2 hours.

After letting out the water and blowing out the conduit, the conduit wasfound to be much more impervious (possible excess pressure about 0.6bar).

Hereupon, cleaning was carried out by means of abrasive jets with asand/waste corundum mixture and a resin internal coating was provided bymeans of the resin mixture specified in Example 1 to which E-glassstaple fibres having a length of about 2 mm and a specific gravity of2.56 g.cm⁻³ had been added.

On completion of the resin internal coating of the conduit part to berepaired (resin discharge at both entrances), after the curing of theresin and after the flushing of the conduit, virtually no more loss ofwater could be detected.

Example 3

The inventors/applicants have installed a simple installation forfurther completion of the method according to the invention, inparticular seal technology (see FIG. 6).

Three layers are poured into the container 6.1 (for example a barrel)with bottom outlet 6.02:6.04 fine sand (.O slashed._(A) to 2 mm) and6.06 gravel (.O slashed._(A) 10 to 20 mm).

When pouring in the layer of gravel 6.06, the sample pipe 6.2 isincorporated into the layer, the horizontal part 6.16 thereof comes torest substantially in the centre of the gravel layer. Filling is thencompleted.

At 6.11 it is possible to connect or install:

the compressed air conduit from the compressor,

the manometer (optionally with display),

gas or steam connection,

the filling pipe for the various sealing mixtures and

a control valve (ball valve), at 2.03:

a control valve

a manometer and

a material trap.

Bores of various diameters can be arranged in the horizontal part 6.16of the sample pipe. Moreover, this "horizontal" part is not alwayshorizontal but can also contain a 90° curve which extendsupwardly/downwardly or to the left/right.

With this simple apparatus, it is therefore possible to simulate inpractice:

gas-impermeable and gas-permeable leaks (in sand or in gravel)

leaks in straight conduit sections and in curves,

blocking with sealed conduit ends or with constantly maintained pressuredifference.

It has been found, after the initial investigations, that dispersionpowders such as EMU® powder 120 FD (BASF), Mowilith® powder DM® 200 P(Hoechst), Vinnapas® dispersion powder (Wacker) or the like, alone ormixed with Portland cement (special cements with high aluminatecontents) are suitable as actual binders.

These agents are disintegrated after the blowing in operation by meansof water, steam and/or by a gas supply (NH₃, CO₂).

Suitable fillers and inert agents for blocking such leakages includeStyropore beads, cork particles, finely ground bentonite, very finelydivided silica (Aerosil^(R)). The extent to which the two last-mentionedmaterials also assist the binder in its effect has not yet beenclarified at present.

Expanded clay can be used as a filling material if the leak is locatedat or round the lowest point of the conduit to be repaired.

Aspiration by means of lances (in the case of gas-impermeable leaks) canbe carried out with the same installation: a tube having a thickenedregion at the front is introduced from 6.13 to in front of the leakagepoint (or is drawn in from the opposite side). As the sealing mixture isbeing blown in, it is mainly deposited in front or in the region of theaspiration (leakage) point. Material which settles in the pipe itselfcan easily be removed again afterwards by the abrasive blowing outoperation.

Example 4

An enlarged test installation was erected: A wooden frame having a widthof 1.8 m, a length of 5.4 m and a height of 0.9 m approximately in eachcase was filled to about 0.2 m with a mixture of gravel and sand (grainsizes 0.5 to 8 mm). An M-shaped coiled pipe from 1" gas pipes was laidonto this bed. As mentioned, said coiled pipe had four parallel lines.To create an artificial pressure drop, the U-shaped fittings between thelines only had a 1/2" .O slashed._(i). In the third line (as viewed inthe direction of flow) one or more 1 cm bores were arranged laterally.The coiled pipe had a respective rising inlet and outlet conduit.

After installation of the coiled pipe, filling was carried out with thesame sand and gravel mixture to a height of about 0.7 m.

The wet blocking mixture was stirred in a 160-1 barrel. It was difficultto achieve satisfactory homogeneity in the mixture. In particular,liquid blocking mixtures consisting of 100 parts by weight of water, 100parts by weight of plastic resin foam particles of 2 to 4 mm and onepart by weight of Aerosil® 90 were examined. The mixing barrel had alower outlet with a check valve. After achieving apparently satisfactoryhomogeneity, a mobile centrifugal pump was connected to conveysuspensions. This produced a Δp of 2 bar excess pressure maximum with adisplacement of about 50 l/min (˜1 l/s).

The connecting conduit from the pump to the entrance conduit of the testinstallation was mobile (metal tube), had a rapid connection (flange)and was provided with a relatively accurate manometer (range 1 to 3 bar,graduation 1/10 bar). The delivery conduit from the test installation,which led to an outlet with preceding filter for the blocking agent, hadan identical manometer and, at the same time, a control valve forregulating the flow characteristics.

The tests were carried out as follows in each case:

After connection of the centrifugal pump, the man at the outletregulated as accurately as possible to 0.5 bar excess pressure and theman at the inlet noted the pressure display on his manometer every 10seconds. It was found that whenever blocking or at least partial closureof the bore occurred, the pressure display at the manometer 1 (asmentioned, the man at manometer 2 watched the outlet excess pressure of0.5 bar which was as constant as possible and also kept an eye on adisplacement which was as constant as possible), was about 0.1 to 0.2bar higher.

A state which, in the opinion of specialists, would have led to agenuine seal of the pipe in the case of subsequent internal charging ofthe pipe with adhesive resin is described as a blockage during theexternal control of the coiled pipe exposed after the test.

In this context, "wet sealing mixtures" consisting of 100 parts byweight of water, ˜8 to 18 parts by weight of rigid EP foam particleshaving a grain size of 2 to 4 mm and a bulk density of <400 kg/m³ aswell as 0.1-1 part by weight of Aerosil® 90 produced the most convincingresults, and the rise in pressure at the manometer 1 (with constant pand v at the outlet) was clearest.

We claim:
 1. A process for the sealing and internal repair of at leastone leak in a system of laid conduits, the process comprising thefollowing steps:(a) introducing a sealant into the conduit by means ofwater, the water cooperating with the sealant to seal the leak; (b)emptying water from the conduit; (c) blowing through the emptied conduitcompressed air that is charged with particles of an abrasive substance;and (d) then internally coating the conduit by introducing and blowinginto it a solvent-free epoxy resin containing a hardener and fibers, thefibers being selected from the group consisting of cellulose fibers,glass fibers, and mixtures thereof.
 2. The process as claimed in claim1, wherein the abrasive substance in step (c) has a hardness of >4 onthe Mohs' scale and an average grain size of <2 mm.
 3. The process asclaimed in claim 2, wherein the cellulose fibers in step (d) have alength of 40±10 mm. and the glass fibers in step (d) have a length of5±3 mm.
 4. The process as claimed in claim 2, wherein the sealant instep (a) comprises a finely divided inert material having a specificgravity of 1±0.8 g.cm⁻³.
 5. The process as claimed in claim 4, whereinthe inert material comprises fine beads having a specific gravity of ≦18g.cm⁻³, particles having a specific gravity of ≧0.2 g.cm⁻³, and veryfinely divided diatomaceous earth having a compactness of approximately1.4 g.cm⁻³.
 6. The process as claimed in claim 2, wherein the leak inthe conduit is located between an inlet portion and an outlet portion ofthe conduit, and wherein step (a) further comprises mixing the sealantwith the water to create a sealant-water mixture and passing thesealant-water mixture through the leaky conduit from the inlet portionto the outlet portion so that a pressure drop between the inlet portionand the outlet portion is maintained at >0.1 bar.
 7. The process asclaimed in claim 1, wherein the cellulose fibers in step (d) have alength of 40±10 mm. and the glass fibers in step (d) have a length of5±3 mm.
 8. The process as claimed in claim 7, wherein the sealant instep (a) comprises a finely divided inert material having a specificgravity of 1±0.8 g.cm⁻³.
 9. The process as claimed in claim 8, whereinthe inert material comprises fine beads having a specific gravity of≦1.8 g.cm⁻³, particles having a specific gravity of ≧0.2 g.cm⁻³, andvery finely divided diatomaceous earth having a compactness ofapproximately 1.4 g.cm⁻³.
 10. The process as claimed in claim 7, whereinthe leak in the conduit is located between an inlet portion and anoutlet portion of the conduit, and wherein step (a) further comprisesmixing the sealant with the water to create a sealant-water mixture andpassing the sealant-water mixture through the leaky conduit from theinlet portion to the outlet portion so that a pressure drop between theinlet portion and the outlet portion is maintained at >0.1 bar.
 11. Theprocess as claimed in claim 1, wherein the sealant in step (a) comprisesa finely divided inert material having a specific gravity of 1±0.8g.cm⁻³.
 12. The process as claimed in claim 11, wherein the inertmaterial comprises fine beads having a specific gravity of ≦1.8 g.cm⁻³,particles having a specific gravity of ≧0.2 g.cm⁻³, and very finelydivided diatomaceous earth having a compactness of approximately 1.4g.cm⁻³.
 13. The process as claimed in claim 12, wherein the fine beadscomprise an inert material comprised of any one of the group of glass,plastic foam parts, cork, clay.
 14. The process as claimed in claim 12,wherein the leak in the conduit is located between an inlet portion andan outlet portion of the conduit, and wherein step (a) further comprisesmixing the sealant with the water to create a sealant-water mixture andpassing the sealant-water mixture through the leaky conduit from theinlet portion to the outlet portion so that a pressure drop between theinlet portion and the outlet portion is maintained at >0.1 bar.
 15. Theprocess as claimed in claim 11, wherein the leak in the conduit islocated between an inlet portion and an outlet portion of the conduit,and wherein step (a) further comprises mixing the sealant with the waterto create a sealant-water mixture and passing the sealant-water mixturethrough the leaky conduit from the inlet portion to the outlet portionso that a pressure drop between the inlet portion and the outlet portionis maintained at > 0.1 bar.
 16. The process as claimed in claim 1,wherein the leak in the conduit is located between an inlet portion andan outlet portion of the conduit, and wherein step (a) further comprisesmixing the sealant with the water to create a sealant-water mixture andpassing the sealant-water mixture through the leaky conduit from theinlet portion to the outlet portion so that a pressure drop between theinlet portion and the outlet portion is maintained at >0.1 bar.
 17. Theprocess as claimed in claim 1, wherein the compressed air in step (c) isfiltered when it exits the conduit.